The present invention relates to an energy management system for a hybrid electric vehicle that comprises an electrical machine for vehicle traction drive and recuperative braking, an electrical storage system for storing recuperated energy, and at least one additional vehicle electrical auxiliary device different from said electrical machine. The present invention further relates to a fuel saving method for said hybrid electric vehicle.
The overall aim of energy management systems for hybrid electric vehicles is to manage electrical power consumption and power recuperation to lower overall fuel consumption and emissions, and improving vehicle drivability.
Document US 2005/0274553 A1 shows a predictive energy management system for hybrid electric vehicles which, based on predicted driving cycles and terrain, selects a power command to operate an electric motor and an engine for the purpose of achieving better fuel economy and lower emissions. Further improvements with respect to fuel consumption and engine emission are however desired.
It is desirable to provide an inventive energy management system for a hybrid electric vehicle that brings about further improvements with respect to fuel consumption and engine emission, which vehicle comprising an electrical machine for vehicle traction drive and recuperative braking, an electrical storage system ESS for storing recuperated energy, and at least one additional vehicle electrical auxiliary device different from said electrical machine. According to an aspect of the invention, an energy management controller is arranged to, upon establishing a potential for increased amount of recuperated energy during a predicted future downhill descent, direct electrical power from said ESS to said at least one additional electrical auxiliary device for the purpose of reducing the electrical charge level of the ESS, such that an increased amount of energy may be recuperated and stored in said ESS during said predicted future downhill descent.
According to another aspect of the invention, a fuel saving method for a corresponding hybrid electric vehicle is provided, which method comprises the steps of establishing a potential for increased amount of recuperated energy during a predicted future downhill descent, and subsequently directing electrical power from said ESS to said at least one additional electrical auxiliary device for the purpose of reducing the electrical charge level of the ESS, such that an increased amount of energy may be recuperated and stored in said ESS during said predicted future downhill descent.
The inventive system and method is based on intelligent use of a predicted future travel path for increasing the anion of recuperated energy during recuperative braking of the vehicle. Without the inventive solution, there is a risk that the ESS may become fully charged during a downhill descent, whilst further braking of the vehicle is required. Moreover, the inventive system does not need to operate the electrical machine for reducing the electrical charge level of the ESS prior to arrival at the predicted descend, but is instead arranged to direct electrical power from said ESS to said at least one additional electrical auxiliary device. The inventive solution thus provides an alternative solution for reducing the electrical charge level of the ESS that is independent of travel path. The inventive solution also presents a plurality of additional electrical auxiliary devices that may be powered with electrical energy from the ESS, thereby increasing the freedom of selection of which power consumer to use, dependent on current and predicted future circumstances. The plurality of additional electrical auxiliary devices also facilitate a relatively large power consumption rate that might be required for reducing the electrical charge level of the ESS at a sufficiently high rate.
The potential for increased amount of recuperated energy is preferably established if an estimated amount of recuperated energy generated by recuperative braking during said predicted future downhill descent exceeds the estimated remaining maximal allowed storage capacity of the ESS. By comparing estimated amount of recuperated energy with estimated remaining maximal allowed storage capacity of the ESS, an efficient tool for determining energy management strategy is provided. Estimation of current SOC of the ESS may be performed by means of a battery management system.
The estimated amount of recuperated energy generated by recuperative braking during said predicted future downhill descent is preferably divided into a first portion that is intended to power at least one additional vehicle electrical auxiliary device during said downhill descent, and a second portion that is intended to be stored in said ESS, and the potential for increased amount of recuperated energy is preferably established if said second portion of said recuperated energy exceeds the estimated remaining maximal allowed storage capacity of the ESS. Direct operation of at least one additional vehicle electrical auxiliary device by recuperated energy results in improved fuel efficiency, because conversion losses upon charging and discharging of the ESS is reduced. Increased flexibility with respect to type and quantity of direct power consumers of recuperated energy is also provided.
The establishment of said potential for increased amount of recuperated energy preferably also takes into account predicted future travel path altitude information up to the start of said predicted future downhill descent.
Additional traction drive by the electrical machine during an uphill path segment in front of the predicted descent might otherwise give an incorrect estimate of the state of charge of the EES at the start of the predicted descent.
The estimated remaining maximal allowed storage capacity of the ESS is preferably determined taking into account an estimated state of charge of said ESS at the start of said predicted future downhill descent.
The at least one additional vehicle electrical auxiliary device is preferably formed by any of a heating system, ventilation system, air conditioning system, starter battery, air compressor, exhaust emission reducing system, engine cooling system, engine lubrication system, steering system, hydraulic or kinetic energy storage systems.
The at least one additional vehicle electrical auxiliary device is preferably coupled to a low voltage network, in particular a 6-50 volts network, or the at least one additional vehicle electrical auxiliary device is preferably coupled to a high voltage network, in particular a 100-1000 volts network. The low voltage network is suitable for relatively low power applications, whereas the high voltage network is suitable for relatively high power applications.
The future downhill descent is preferably predicted by means of a vehicle future travel path prediction system, which may comprise a GPS in combination with travel path altitude information, or travel path recognition system with travel path altitude information, or a combination thereof.
The predicted future downhill descent is preferably established if the start thereof is located within a certain distance from the vehicle. The distance may for example be up to 2 km, preferably up to 10 km, more preferably up to 20 km.
The energy management controller may preferably override normal control of said at least one additional vehicle electrical auxiliary device upon powering of said at least one additional electrical auxiliary device by electrical energy from said ESS for the purpose of reducing the electrical charge level of the ESS. Some of the additional vehicle electrical auxiliary devices are during normal control periodically operated, or operated to attain a target value, or operated to be positioned in a predefined range. The time of normal operation does however rarely coincide with the time of operation required by the energy management system. Therefore, the energy management system may override the normal control.